“Guys have learned ways to be discreet about it, out of necessity,” Hangartner tells The Post.

“I’ve never understood why there’s not a porta-potty on an NFL sideline. You’re out there for an hour and a half with no bathroom breaks.”

A few desperate ballers go further: “Some guys will sit on a bench, on a towel, and just go, then hose themselves off with ice water and move on,” Hangartner revealed.

Gross had the good fortune to play in the Super Bowl in his rookie season, making the surreal experience of adapting to life in the NFL that much more so.

He tells The Post about a strange moment from that 2003-04 season, which ended with the Panthers’ 32-29 loss to the New England Patriots in Super Bowl XXXVIII.

“We went to Philly for the NFC Championship Game at the end of January. I had heard a lot about Philly and their fans, but as a rookie, I never really understood it. As we’re driving into the stadium, snowballs start erupting down the side of the bus. I’m looking up going, ‘What’s happening? Who’s attacking us?’ ”

It was rowdy Philadelphia Eagles fans. One was particularly memorable.

“I saw an old grandma, had to be 70-something, double middle-finger flipping off our bus. That told me right there, this is not college football ,” Gross said.

Gross also had to deal with craziness from teammates, recalling the time a veteran who would sniff smelling salts to psych himself up shot some up Gross’ nose ahead of a Giants game: “It got me so nauseous that I had to throw up before we took the field.”

Rookies learn the hard way to watch their surroundings — including TV cameras. While networks aren’t likely to broadcast players urinating, “I’ve been caught on camera full-on picking my nose on the sidelines,” Gross said.